(1) Field of the Invention
This invention relates to methods for fabricating a fuser roller used for electrographic image formation devices.
(2) Description of Related Art
Electrographic image formation devices, such as copiers, laser printers or facsimile machines, are equipped with various kinds of rollers including a feed roller, a transfer roller, a fuser roller, a pressure roller and a delivery roller. Of these rollers, the fuser roller is a roller for introducing a paper or the like onto which a toner image has been transferred between itself and the pressure roller to fuse the toner image to the paper or the like. Such a fuser roller is generally constructed so that cylindrical shafts are extended from both ends of a cylindrical body and has a built-in heat source such as a halogen lamp.
An exemplary method for fabricating such a fuser roller will be now described with reference to FIGS. 6 to 8.
As shown in FIG. 6, first prepared are a cylindrical body 12 having a through hole 11 and a shaft member 15. The cylindrical body 12 is obtained by cutting to length an elongated pipe member 14 which is a draw member having a through hole 13 and made of metal such as an aluminum alloy, and has openings at both ends. The shaft member 15 is a forged part of stainless steel, for example, and is composed of a disk portion 16 abutted on each opening end of the through hole 11 of the cylindrical body 12, a shaft portion 17 of circular contour extending integrally from one side face of the disk portion 16, and an annular fitting portion 18 extending integrally from the other side face of the disk portion 16. A through hole 19 is formed through the disk portion 16 and the shaft portion 17.
Next, as shown in FIG. 7, the cylindrical body 12 is set to a rotating jig (not shown), the shaft member 15 is set to a pressing jig (not shown), and the annular fitting portion 18 of the shaft member 15 is fitted into one opening end of the through hole 11 of the cylindrical body 12. In this state, the axes X1 of the cylindrical body 12 and the shaft member 15 are matched with each other, and the shaft member 15 is pressed against the cylindrical body 12 while the cylindrical body 12 is rotated on the axis X1. The shaft member 15 is thus joined integrally with the cylindrical body 12 by friction welding. Also at the other opening end of the through hole 11 of the cylindrical body 12, another shaft member 15 is likewise joined integrally with the cylindrical body 12 by friction welding. As a result, as shown in FIG. 8, a pair of shaft members 15 are joined concentrically and integrally with the cylindrical body 12 at both ends of the through hole 11, thereby obtaining a fuser roller 20 in which the through holes 11 and 19 are communicated with each other. The through hole 11 of the cylindrical body 12 forms an accommodation space which accommodates a heat source such as a halogen lamp. Since this prior art, however, does not relate to any publicly described invention, there is no information concerning prior art documents to be cited (this prior art is hereinafter referred to as Prior Art 1).
As an alternative fabrication method, there is a method comprising: first setting a cylindrical metal body to a rotating jig; machining both end portions thereof with rotation to form thin-walled portions; and plastically forming the thin-walled portions with a punch in plural steps to form shafts at both ends of the body (see, for example, Patent Document 1).
[Patent Document 1]
Japanese Unexamined Patent Publication No. 2002-123103 (page 4, FIGS. 3 and 4)
Since the above fabrication method of Prior Art 1 uses two kinds of members, i.e., the cylindrical body 12 and the shaft member 15, it is necessary to fabricate these members separately and to join the two kinds of members separately fabricated with each other. To satisfy this necessity, three kinds of processing machines are required, resulting in elevated equipment expenses. In addition, three processing steps are required, presenting problems of much production time and poor production efficiency.
On the other hand, according to the fabrication method of Patent Document 1, shafts are formed by machining both end portions of the cylindrical body. Therefore, there is no need for the step of joining two kinds of members with each other as done in Prior Art 1. As a result, the number of processing machines is correspondingly decreased thereby reducing equipment expenses. In addition, the number of processing steps is correspondingly decreased thereby enhancing production efficiency. This method, however, still employs different processing techniques of machining process and plastic formation with a punch. Therefore, even though this method can reduce equipment cost, it still necessitates two kinds of processing machines and its equipment cost is quite high. Furthermore, this method requires two processing steps and leaves room for improvement in production efficiency.
In addition, according to the fabrication method of Patent Document 1, both end portions of the cylindrical body are first machined, and the thin-walled parts created by machining are then plastically formed with a punch. Therefore, though the shafts are somewhat increased in thickness by plastic formation, they cannot obtain a sufficient thickness due to initial reduction by machining as compared with the case of undergoing no machining process, resulting in reduced rigidity. If allowance is previously provided for machining instead in order to obtain a sufficient thickness of the shafts, a thick cylindrical body must be prepared, which invites elevated unit cost of the fuser roller.
The present invention has been made in view of the foregoing points, and therefore an object of the present invention is to reduce equipment cost, further enhance production efficiency and fabricate a fuser roller at low cost by allowing a fuser roller to be fabricated with a processing machine of one kind for one pipe member.
The present invention is characterized, in order to attain the above object, by utilizing a spinning process of necking a cylindrical workpiece by pressing a forming roller against the outer periphery of the workpiece while rotating the workpiece, and specifically takes the following solutions.
More specifically, the invention claimed in claim 1 is characterized by comprising: heating a cylindrical metal blank with its both ends open over predetermined regions starting from both opening ends; and then necking the heated regions of the blank by moving a forming roller with rotation on the heated regions of the blank through the external pressing of the forming roller against the heated regions of the blank being rotated on its axis to draw form sidewalls integrally at both ends of a cylindrical body of the blank having an accommodation space for accommodating a heating element, respectively, and draw form cylindrical shafts integrally with the sidewalls in concentric relation with the body, respectively, thereby obtaining a fuser roller, said cylindrical shafts each having a shaft space communicating with the accommodation space of the body.
With the above constitution, according to the invention claimed in claim 1, the fuser roller is formed simply by necking both end portions of a single workpiece of a blank with a forming roller while rotating the workpiece. Therefore, the fuser roller can be obtained with a single processing machine without the joining of two members and any combination of different processing techniques, which reduces equipment cost. Furthermore, the fuser roller can be formed in a single processing step, which further enhances production efficiency. Moreover, since the portions to be formed into shafts are not machined, there is no need for thickening the blank in order to make allowance for machining, thereby obtaining the fuser roller at lower cost.
The invention claimed in claim 2 is characterized in that in the invention of claim 1, each said shaft is draw formed in a larger thickness than the body.
With the above constitution, according to the invention claimed in claim 2, the shaft is increased in rigidity thereby enhancing its bearing strength.
The invention claimed in claim 3 is characterized in that in the invention of claim 1, each said sidewall is extended at its inner surface toward the inside of the body in a manner to be gradually increased in thickness in proceeding from the body to the shaft so that the portion of the sidewall corresponding to the periphery of the shaft is the thickest portion thereof.
With the above constitution, according to the invention claimed in claim 3, the thickest portion can increase the joining strength of the sidewall with the shaft, and the sidewall, which gradually increases its thickness in proceeding from the body to the shaft, can increase the integrity of the shaft with the body. In addition, since the sidewall extends toward the inside of the body, this prevents the sidewall from interfering with a bearing for rotatably supporting the shaft.